API Std 618-2007 Reciprocating Compressors for Petroleum, Chemical, and Gas Industry Services

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Figure G-3—Distance Piece and Packing Arrangements

B B C B

D P

F G

P P C B

Frame end

Crosshead

Crosshead guide

Inboard

distance piece

Access

opening

Outboard

distance piece

Access

opening

Oil wiper packing

(see note 3)

Partition

(When required)

Oil slinger

Piston rod

Pressure

packing

2 (see note 4)

Intermediate

partition

(When required)

Piston

Cylinder

2 (see note 4)

B B C B

D P

F G

C B

Frame end

Crosshead

Crosshead guide

Inboard

distance piece

Access

opening

Outboard

distance piece

Access

opening

(optional)

Oil wiper packing

(see note 3)

Partition

(When required)

Intermediate

partition

(When required)

Oil slinger

Piston rod

Pressure

packing

(When required)

Piston

Cylinder

B B

F G

C B

Frame end

Crosshead

Crosshead guide

Distance piece

Access

opening

Oil wiper packing

(see note 3)

Partition

(When required)

Oil slinger

Piston rod

Pressure

packing

(When required)

Piston

Cylinder

F G

C BB

Frame end

Crosshead

Crosshead guide

Distance

piece

Access

opening

Oil wiper packing

(see note 3)

Partition

Piston rod

Pressure

packing

(When required)

Piston

Cylinder

TYPE A

SHORT SINGLE-COMPA RT MENT DISTANCE PIECE

(MAY BE INTEGRAL WITH CROSSHEAD GUIDE OR CRANK END HEAD)

TYPE B

LONG SINGLE-COMPAR T MENT DISTANCE PIECE

(SUFFICIENT LENGTH FOR OIL SLINGER TRAVEL)

TYPE D

SHORT TWO-COMPA RTMENT OR DOUBL

E DISTANCE PIECE ARRANGEMENT

(INBOARD DISTANCE PIECE OF SUFFICIENT LENGTH FOR OIL SLINGER TRAVEL)

TYPE C

LONG TWO-COMPAR TMENT OR DOUBLE DISTANCE PIECE ARRANGEMENT

(INBOARD AND OUTBOARD DISTANCE PIECES EACH OF SUFFICIENT

LENGTH FOR OIL SLINGER TRAVEL)

Legend:

1. Seal or buﬀer packing, distance piece

2. I

ntermediate seal or buﬀer packing, distance piece (solid access

covers required)

Connections (see 6.12.2 for sizes):

A Vent, distance piece

B Purge, buﬀer, or pressure, packing or distance piece

C Lube, pressure packing

D Drain, distance piece

E Coolant out, pressure packing

F Coolant in, pressure packing

G Common vent and drain, pressure packing

P Plugged connection

Notes:

1. See 6.10 and 6.13.1.3.

2. The orientation of distance-piece and packing-ﬂange/case connections

may vary depending on the individual distance piece and the type of

packing case used.

3. The oil wiper packing may be located in the distance piece on the other

side of the partition from that shown, and would be an integral assembly

with the seal or buﬀer packing (1).

4. The intermediate seal or buﬀer packing (2) may be located in the outboard

distance piece on the other side of the partition from that shown.

RECIPROCATING COMPRESSORS FOR PETROLEUM, CHEMICAL, AND GAS INDUSTRY SERVICES 151

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Figure G-4—Typical Self-Contained Cooling System for Piston Rod Pressure Packing

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0ACKING

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#YLINDER

0RESSURE

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#ONSOLECOOLANT

SUPPLYCONNECTION

#ONSOLECOOLANT

RETURNCONNECTION

6ENTTOA

SAFEAREA

#ONSOLEBOUNDARY

0ACKINGCOOLINGCONSOLEFORCOOLANT

03,

0!,

-)#2/.

&),4%2

$RAIN

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CLEANOUT

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)NLETCONNECTION

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CONNECTION

Note 1: The instrumentation shown is the minimum required. The purchaser may wish to specify additional devices.

Note 2: For cooling medium other than water system design shall be mutually agreed upon between purchaser and the vendor.

Note 3: See 6.13.

Note 4: If a packing cooling console is not supplied, individual strainers are required (see 6.13.2.6).

Note 5: Cooler to have vents and drains on both shell and tube side.

Note 6: Normal level is above the highest point of the piping on the compressor cylinders.

Note 7: The system shown is typical: more or less equipment may be provided.

152 API STANDARD 618

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Figure G-5—Typical Pressurized Frame Lube Oil System

CRANKCASE OIL RESERVOIR

Console boundary

Vent

Drain

Oil

ﬁlter

Vent

Drain

Oil

ﬁlter

TCV

PDAH

PDSH

AUX. PUMP

OIL

COOLER

Motor

PRV

Console

return connection

PI PSLPSL

PAL

PSLL

Shutdown

Aux. pump start

Frame

breather

PRV

LAL

LSL

Drain

OWS

Crankcase

drain

Inlet

strainer

Main

pump

Main

drive

motor

Heater

Console

supply

connections

Notes:

1. Instrumentation shown is

the minimum required. The

purchaser may wish to

specify additional devices.

2. See 6.14.2.

3. Cooler to have vents and

drains on both shell and

tube side.

4. The system shown is

typical: more or less

equipment may be provided.

5. Check valve with RO on

main pump is optional. The

RO is for priming the main

pump.

6. See 6.14.2.4.

7. Six-port continuous-ﬂow

transfer valve, manually

operated.

Note 7

Note 6

Note 5

Note 3

Manual

override

Oil system

extended to driver

(if speciﬁed)

Gravity drain to

crankcase (when oil

system extended to

driver is speciﬁed)

RECIPROCATING COMPRESSORS FOR PETROLEUM, CHEMICAL, AND GAS INDUSTRY SERVICES 153

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Figure G-6—Conceptual Direct Rod Connection

Body (Crosshead)

Bolt (Piston rod)

Location of

thread-root prestress-

force

Jambnut

Figure G-7—Conceptual Indirect Rod Connection

Body (Crosshead)

Bolt (Piston rod)

Figure G-8—Conceptual Indirect Clamped Rod Connection

Body (Crosshead)

Bolt (Piston rod)

Clamping Nut

154 API STANDARD 618

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Figure G-9—Tightening Diagram (Bolt–Bracing–Diagram)

Force

Operating Force

during compression stroke

Prestress Force

of Fastening

Operating Force

during tension stroke

Body (Crosshead)

characteristic

Bolt (Piston rod)

characteristic

Elongation

Definitions: F

= Prestress of the Fastening

= Operating Force (under MAWP-condition, or at maximum allowable continuous rod load)

= amplitude of the alternating Force (in the bolt-shaft and thread)

= max Force (in the bolt-shaft and thread)

= min remaining Force in the fastening

max

= max stress in the thread-root or any other area of the bolt due to F

= alternating Stress at the thread-root section due to F

RECIPROCATING COMPRESSORS FOR PETROLEUM, CHEMICAL, AND GAS INDUSTRY SERVICES 155

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No reproduction or networking permitted without license from IHS

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Provided by IHS under license with API

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157

Annex H

(Informative)

Table H-1—Material Specifications for Reciprocating Compressor Parts

Part Material Form

Frame Cast iron Cast

Crankshafts Steel Forged

Connecting rods Steel Forged

Crossheads Steel Bar stock, forged, or cast

Ductile iron Cast

Crosshead pins Steel Forged or bar stock

Distance pieces Cast iron Cast

Cylinders Steel Cast, forged, or fabricated

Stainless steel Cast or fabricated

Nodular iron Cast

Gray iron Cast

Cylinder liners Steel Tubing

Stainless Steel Cast

Ni-resist Cast

Nodular iron Cast

Gray iron Cast

Cylinder heads Steel Cast, forged, or fabricated

Stainless steel Plate

Nodular iron Cast

Gray iron Cast

Pistons Steel Forged, cast, bar stock, or fabricated

Cast iron Cast

Aluminum Forged or cast

Piston rods and tailrods Steel Forged or bar stock

Stainless Steel Bar stock

Piston rod nuts Steel Forged or bar stock

Stainless Steel Forged or bar stock

Valve seats and guards Steel Plate or bar stock

Stainless steel Plate, bar stock, or cast

Nodular iron Cast

Cast iron Cast

Valve plates Stainless steel Plate

Non-metallic Molded

Va l ve s pr i ngs Steel Drawn

Stainless steel Formed

Packing cases Steel Bar stock

Stainless steel Bar stock

Cast iron Cast

Packing case flange Steel Forged, bar stock, or plate

Piston rings, wear bands, and packing rings Metallic Cast or Bar Stock

Non-metallic Molded or Sintered

Materials for Major Component Parts

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159

Annex I

(informative)

Distance Piece Vent, Drain and Buffer Systems to Minimize Process Gas Leakage

I.1 Scope

This annex contains a general philosophy for the design of reciprocating compressor distance piece vent, drain, and gas buffer

systems, which are typical of systems commonly used to minimize process gas leakage. This annex is not intended to cover all

possible situations; rather, it focuses on providing an approach, which can be used to design successful systems.

Note: The piping, tubing, and components external to the distance piece may be supplied by either the purchaser or vendor. It is good practice

for the vendor and purchaser to discuss the vent and drain system, and agree on its design (see 6.12.2).

Instrument piping and valving details are not shown on typical schematics. Such requirements, including on-line testing

requirements, should be agreed upon by the purchaser and vendor.

I.2 Abbreviation and Symbols

The abbreviations and symbols used in the schematics in this annex are shown in Annex G.

I.3 The Purpose of Distance Piece Vent, Drain and Buffer systems

A distance piece vent and drain system working in conjunction with packing, buffer system and partitions, accomplishes several

functions, including:

a. confining and collecting the normal leakage from compressor rod pressure packing and carrying the leakage to a safe location;

b. preventing process gas, toxic gas or hazardous gas leakage into the area around the machine;

c. preventing contamination of the crankcase lube oil;

d. atmospheric fugitive emission control;

e. confining and collecting large leakage in the event of compressor pressure packing failure, and directing the leakage to a safe

location;

f. helping to prevent an explosive atmosphere from developing in the crankcase;

g. preventing excessive liquid accumulation in the distance piece;

h. avoiding gas leakage to sewer systems;

i. allowing the operator to monitor and determine the condition of compressor rod pressure packing.

I.4 Minimizing Process Gas Leakage

Figures I-1 and I-2 illustrate the arrangement of two typical distance piece types that may be used when it is necessary to reduce

the leakage of process gas to a minimum. The accompanying packing detail drawing, Figure I-3, shows the arrangement of the

packing rings and the direction of flow and typical pressures of the buffer gas.

Side-loaded packing rings provide constant mechanical axial loading towards the sealing face of the cup. This mechanical axial

loading, added to a buffer gas pressure at least 1 bar higher than the disposal pressure, hold the rings positively against their

sealing faces minimizing buffer gas leakage and, at the same time, assures that all the process gas that leaks past the cylinder

pressure packing cups will be forced out into the disposal system (for example, the flare) through the vent.

When proper differential buffer gas pressures are maintained, process gas leakage into the distance pieces is minimal; process gas

is prevented from entering the compressor frame. To minimize gas emissions, special packing and long distance pieces should be

specified (see 6.13.1.6).

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160 API STANDARD 618

I.5 Design Consideration

In addition to meeting the purposes described in I.2 the following factors should be considered when designing in designing a

distance piece vent, drain and buffer system:

a. Small diameter vent and drain piping will tend to foul and corrode over time, inhibiting their function. Consider using large

[e.g., DN 50 (NPS 2)] vent and drain headers and corrosion-resistant materials.

b. On two-compartment distance piece systems, external cross connections between the inner and outer compartment vents and

drains should be avoided.

c. On multiple machine systems, it should be possible to isolate each machine for maintenance.

d. Effective control of gas leakage requires the specification of gasketed solid metal covers on distance pieces (see 6.12.2.1).

e. Where vents, drains, liquid collection pots and distance pieces are connected to disposal systems, such as a flare or closed

drain system, they should be designed to withstand the maximum disposal system pressure (e.g., flare back pressure under

relieving conditions). See 6.12.2.3.

Note: Distance pieces are typically designed for a maximum gauge pressure of 2 bar (25 psi). Special designs are required for higher pressures.

f. Typically, the common vent and drain from the pressure packing (connection G in Figure I-1 and I-2) will be carrying a

mixture of liquid and gas. The system should be designed to separate these phases to avoid liquid blockage of the vent system.

g. Leaks from the stems of valve unloaders and clearance pockets may also need to be collected and controlled. These can be

integrated with the distance piece vent and drain system.

h. There is concern about the reliability of check valves in safety situations, particularly in low pressure systems such as distance

piece vent and drain systems where there is any mixture of gas and liquids. Check valve use should be avoided, where possible.

i. Except for the pressure packing combined vent and drain, which is a pressure driven flow, separate vent and drain lines are

necessary between the distance piece and liquid collection pot to pressure balance the system and allow free drainage. Sloped

headers, without pockets, assist draining.

j. Large diameter tubing [20 mm (

/4 in.) OD minimum] can be used between the individual distance pieces and the vent and

drain headers. This usually results in a neat, easily maintained installation compared to a piping system.

k. Manifolding and cross-connections with drains and blowoffs from other equipment should be avoided.

l. The buffer gas purge pressure must be limited to the maximum allowable pressure for the distance piece components (see

6.10.4). Some buffer gas will flow into the compressor frame. Frame venting must allow an outlet for this flow (see Figure G-5).

m. Pneumatic trip systems internal to the frame (e.g., crosshead pin temperature) should be energized with nitrogen rather than air

to assist in maintaining an inert atmosphere in the crankcase.

n. Effective establishment of an inert atmosphere in the crankcase will necessitate special maintenance safety procedures.

o. Where climatic conditions require, drains should be heat-traced and insulated.

p. Under total packing failure, it should not be possible to over-pressure the distance piece (see 6.10.4 and 6.10.5). If the vent area

is not sufficient, additional venting to a safe location by way of emergency pressure relief valves or spring-loaded pressure relief

doors may be required.

q. Buffer gas purge rates are typically sized for a flow rate of 0.03 m

/h (10 standard ft

/h) per packing set [may reach 0.2 m

(65 standard ft

/h) per packing set on startup] and are fitted with flow indicators.

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